1. Field of the Invention
This invention relates to a bicycle speed change lever assembly, and more particularly to improvements in the lever assembly for operating a derailleur to shift a drive chain from one to another of diametrically different sprockets of a multiple freewheel or a multiple chainwheel. More specifically, the invention is directed to a bicycle speed change lever of the type that is readily applicable to different types of derailleurs by a simple change in operational mode.
2. Prior Art
As is well-known, bicycles are equipped in many cases with a speed change mechanism to enable cycling suited to a particular road condition or to a cyclist's desire. Such speed change mechanism includes for example a rear derailleur of the type that comprises a shiftable cage rotatably supporting a pair of guide pulleys and a control mechanism such as a parallelogrammic linkage mechanism for displacing the guide pulleys laterally of a multiple freewheel to shift a drive chain engaging with the pulleys from one sprocket to another of the freewheel. The speed change mechanism may further comprise a pair of parallel guide plates and a control mechanism such as a parallelogrammic linkage mechanism, similar to that of the rear derailleur, for displacing the guide plates laterally of a multiple chainwheel to shift the drive chain from one sprocket to another of the chainwheel.
The movement of the guide pulleys or the guide plates is controlled by a control lever which is operatively connected to the parallelogrammic linkage mechanism via a control cable a part of which extends along a cable winding groove formed in an outer circumference of a cylindrical boss portion of the control level which has a handle portion extending radially from the boss portion. The control lever is pivotally mounted at the boss portion to a suitable part of a bicycle frame. When the control lever is pivoted, the cable is wound up along the winding groove onto the boss portion or paid out therefrom to vary tension of the cable thereby to regulate the parallelogrammic linkage so that it is correspondingly deformed to bring the guide pulleys or the guide plates to a lateral position predetermined by the pivotal position of the control lever.
Normally, the control lever is pivoted steplessly. It is, thus, quite difficult for an unskillful cyclist to operate the control lever to bring the guide pulleys or the guide plates to an optimum position relative to each sprocket of the multiple freewheel or the multiple chainwheel. As such, the guide pulleys or the guide plates are sometimes stopped erroneously at a position intermediate two adjacent sprockets, failing to effect intended shifting of the drive chain onto a selected sprocket of the multiple freewheel or the multiple chainwheel. This gives rise to objectionable gear noises or unwanted vibration of the drive chain.
In order to improve the maneuverability of the control lever, it has been proposed to incorporate into the lever assembly a click mechanism which serves to clickingly hold the control lever at each of predetermined pivotal positions, as disclosed for example in Japanese Patent Applications Laid-open Nos. 60-209376 (Application No. 59-67162 filed Apr. 3, 1984, Inventor: Masashi Nagano), 60-209377 (Application No. 59-67163 filed Apr. 3, 1984, Inventor: Masashi Nagano), and 61-33380 (Application No. 59-156222 filed July 25, 1984, Inventor: Masashi Nagano). With the use of the click mechanism, any cyclist, skilled or unskilled, can easily operate the control lever to bring the guide pulleys or the guide plates accurately to an optimum position immediately under a selected sprocket of the multiple freewheel or the multiple chainwheel and thereby conduct desired speed change.
The conventional lever assembly incorporating the click mechanism enables pivotal movement of the control lever only in a single click pattern and is thus applicable only to a single type of derailleur associated with a specific type of multiple freewheel (or multiple chainwheel). In other words, the known clicking lever assembly, if designed to suit a five-sprocket freewheel for example, is no longer applicable to a seven-sprocket freewheel for example. Further, the clicking lever assembly becomes inoperative if the associated derailleur is replaced by another type of derailleur since the two derailleurs differ from each other in the amount of displacement of respective guide pulleys per unit amount of pivotal movement of the control lever.